The present invention relates to a method for forming a metal contact of a semiconductor device, and particularly to a method for forming a metal contact to improve the reliability of an electric wiring by forming a double thin metal layer on a contact plug metal, so that it is not directly connected with a photoresist film.
Conventionally, to form contacts in contact holes having various depths in a semiconductor device, firstly a tungsten is selectively deposited on a contact hole exposing a silicon substrate or a conducting layer opened by a CVD (Chemical vapor deposition) process using WF.sub.6 H.sub.2, SiH.sub.4 gas, etc., and then an aluminum alloy is deposited on the entire structure. However, because the tungsten is grown from the bottom of a silicon layer or a conducting layer at the same speed irrespective of the depth of the contact hole, it is very difficult to fill completely the tungsten in a deep contact hole.
Therefore, It is known to form a deep contact hole and a shallow contact hole separately and to respectively deposit the tungsten in the contact holes.
In this method, firstly the deep contact hole is formed by means of a contact mask and a tungsten is deposited on an exposed silicon layer or an exposed conducting layer of the contact hole by a selective deposition process.
Next, the shallow contact hole is formed by means of another contact mask and then the aluminum alloy is deposited on the entire structure.
However, in the above conventional method, because a photoresist may remain on the upper part of the tungsten of the first contact hole, or a natural oxide or a tungsten oxide layer may be formed on the surface of the tungsten, there occurs the problem that contact resistance is increased.
Accordingly, it is an object of the present invention to provide a method for forming a metal contact for a semiconductor device in order to improve the reliability of electric wiring by forming a double thin metal layer on a contact plug metal, so that it is not directly connected with a residual photoresist.